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User Contributed Notes 21 notes

Since this is only mentioned in the footnote of the output of one of the examples, I feel it should be spelled out:

* THIS FUNCTION ONLY VISITS LEAF NODES *

That is to say that if you have a tree of arrays with subarrays of subarrays, only the plain values at the leaves of the tree will be visited by the callback function. The callback function isn't ever called for a nodes in the tree that subnodes (i.e., a subarray). This has the effect as to make this function unusable for most practical situations.

If you are wanting to change the values of an existing multi-dimensional array, as it says above in the note, you need to specify the first argument as a reference. All that means is, be sure to precede the $item variable with an ampersand (&) as in the good_example below.

Unfortunately the PHP example given doesn't do this. It actually took me a while to figure out why my function wasn't changing the original array, even though I was passing by reference.

Here's the tip: Don't return any value from the function! Just change the value of $item that you passed in by reference. This is rather counter-intuitive since the vast majority of functions return a value.

Returning a value from your function does work if you pass by reference and modify $item before you return, but you will eat up memory very, very fast if you try it, even on an example as small as the one here.

One other silly thing you might try first is something like this:

<?php// Resist the urge to do this, it doesn't work.$filtered = array_walk_recursive($unfiltered,'filter_function');?>

Of course, $filtered is just TRUE afterwards, not the filtered results you were wanting. Oh, it ran your function recursively alright, but changed all the values in the local function scope only and returns a boolean as the documentation states.

since PHP 5.3.0, you will get a warning saying that "call-time pass-by-reference" is deprecated when you use & in foo(&$a);. And as of PHP 5.4.0, call-time pass-by-reference was removed, so using it will raise a fatal error.

The description says "If funcname needs to be working with the actual values of the array, specify the first parameter of funcname as a reference." This isn't necessarily helpful as the function you're calling might be built in (e.g. trim or strip_tags). One option would be to create a version of these like so.

The downside to this approach is that you need to create a wrapper function for each function you might want to call. Instead, we can use PHP 5.3's inline function syntax to create a new version of array_walk_recursive.

<?php
/**
* This function acts exactly like array_walk_recursive, except that it pretends that the function
* its calling replaces the value with its result.
*
* @param $array The first value of the array will be passed into $function as the primary argument
* @param $function The function to be called on each element in the array, recursively
* @param $parameters An optional array of the additional parameters to be appeneded to the function
*
* Example usage to alter $array to get the second, third and fourth character from each value
* array_walk_recursive_referential($array, "substr", array("1","3"));
*/
function array_walk_recursive_referential(&$array, $function, $parameters = array()) {
$reference_function = function(&$value, $key, $userdata) {
$parameters = array_merge(array($value), $userdata[1]);
$value = call_user_func_array($userdata[0], $parameters);
};
array_walk_recursive($array, $reference_function, array($function, $parameters));
}
?>

The advantage here is that we only explicitly define one wrapper function instead of potentially dozens.

I needed to add or modify values in an array with unknown structure. I was hoping to use array_walk_recursive for the task, but because I was also adding new nodes I came up with an alternate solution.

<?php

/** * Sets key/value pairs at any depth on an array. * @param $data an array of key/value pairs to be added/modified * @param $array the array to operate on */function setNodes($data, &$array) {$separator = '.'; // set this to any string that won't occur in your keysforeach ($data as $name => $value) { if (strpos($name, $separator) === false) {// If the array doesn't contain a special separator character, just set the key/value pair. // If $value is an array, you will of course set nested key/value pairs just fine.$array[$name] = $value; } else {// In this case we're trying to target a specific nested node without overwriting any other siblings/ancestors. // The node or its ancestors may not exist yet.$keys = explode($separator, $name);// Set the root of the tree.$opt_tree =& $array;// Start traversing the tree using the specified keys.while ($key = array_shift($keys)) {// If there are more keys after the current one...if ($keys) { if (!isset($opt_tree[$key]) || !is_array($opt_tree[$key])) {// Create this node if it doesn't already exist.$opt_tree[$key] = array(); }// Redefine the "root" of the tree to this node (assign by reference) then process the next key.$opt_tree =& $opt_tree[$key]; } else {// This is the last key to check, so assign the value.$opt_tree[$key] = $value; } } } } }

I decided to add to the previous PHP 4 compatible version of array_walk_recursive() so that it would work within a class and as a standalone function. Both instances are handled by the following function which I modified from omega13a at sbcglobal dot net.

The following example is for usage within a class. To use as a standalone function take it out of the class and rename it. (Example: array_walk_recursive_2)

This function has a serious bug, which is still not fixed as of the PHP 5.2.5 release. After you call it, it can accidentally modify your original array. Save yourself hours of frustration by reading on.

If the array that you walk contains other array elements, they will be turned into references. This will happen even if the callback function doesn't take its first argument by reference, and doesn't do anything to the values.